The present invention relates generally to a resurfacing prosthesis and more specifically it relates to an improved side sliding mini knee prosthesis used for the resurfacing of articular surfaces of tibia and femur, and a surgical method for insertion of said mini implant through a small and minimally invasive direct lateral approach, using templates and a miniature robotic actuator cutting device, without any disruption of extensor mechanism, quadriceps tendon or damage to the cruciate ligaments.
It can be appreciated that knee arthroplasty and resurfacing knee implants have been in use now for many decades. The procedure usually requires the operating surgeon to prepare the end of the tibial and femoral bones to receive the implant. This preparation requires the careful removal of the articular surface and adjacent bone in order to receive the intended implant.
Said preparation requires the use of mechanical bone resection devices such as mills, bone saws or high-speed burrs. In order to accomplish such task, the operating surgeon needs to expose the bone end and protect the surrounding tissue from the aggressive cutting tools.
Typically, knee replacement prostheses comprise several types of implants, where articular surfaces of the knee are removed and replaced with metal and polyethylene components. There has been little change to the basic design of the femoral and tibial components as well as surgical insertion techniques since the initial inception in the mid fifties.
The devices of the prior art attempted to duplicate the geometry of the natural articular femoral and tibial surfaces, where the femoral component have a semicircular C shaped implant device such as depicted in a U.S. Pat. No. 4,224,696. The bicondylar design is similarly disclosed in prior patents by F. Buechel and Pappas in U.S. Pat. Nos. 4,309,778 and 4,470,158. A more recent bicondylar design is described in U.S. Pat. No. D473,307S and U.S. Pat. No. 6,197,064 B1. The prior art describes the bicondylar prosthesis as having a middle patellar groove for the femoropatellar articulation. Other knee implant devices are used to resurface only one femoral condyle such as unicondylar prosthesis described in U.S. Pat. No. 7,141,053; 6,726,724 B2.
The majority of the commonly used knee implants use bone cement as a mean of fixation to the bone. More recently, cementless and bone ingrowth fixation has been introduced and used for the tibial, femoral and patellar surfaces.
Other prior art includes bicondylar resurfacing implant, such as the one described in U.S. Pat. No. 8,114,164 by Zafer Termanini. However, said implant did not allow the use of bone cement as mean of fixation and relied solely on geometry interference between the transverse ridges and the resected bone surfaces. The implant of the present invention will allow the use of bone cement, while still specifically introduced through direct lateral approach.
However, unicondylar implants in general present a high rate of failure due to loosening and dislocation secondary to poor distribution of weight and high concentration of stress over a small surface. Furthermore, almost all the described implants in the above-cited patents are inserted through the invasive conventional anterior approach. Such a surgical approach causes extensive soft tissue disruption and irreparable scarring to major anatomical structures.
Another problem with the conventional surgical approach is the fact that the femoral condyles are approached anteriorly through a medial or lateral parapatellar approaches requiring to laterally displace the patella or dislocate (“flip over”) the patella in order to approach and expose the distal end of the femur and to better visualize the medial and lateral surfaces to be cut. Said dislocation (“flip over”) or lateral displacement of the patella, frequently weakens and damages the insertion of the patellar tendon, causing undue pain in the immediate postoperative period and lengthens post operative physical therapy. Typically, the operating surgeons commonly extend the incision or cut (“snip”) the Vastus medialis muscle in order to facilitate the lateral displacement of the patella. Furthermore, the large sizes of the conventional femoral and tibial components make them difficult to insert through a small and limited incision of the direct lateral approach. The prosthesis of this invention is thinner and much smaller than the conventional total knee femoral component, since it does not resurface the femoropatellar joint.
While conventional devices may be suitable for the particular purpose to which they address, they are, because of their size, not suitable for bicondylar knee resurfacing through a limited direct lateral approach, without disrupting the extensor mechanism, damaging the quadriceps tendon or the cruciate ligaments.
During a conventional total knee replacement, the distal femur is usually resected with five cuts that correspond to the shape of the inner surface of the femoral component. These cuts are commonly performed with a bone-cutting tool, such as a power oscillating saw or a mill that is guided by a cutting block or a template affixed to the bone through the anterior approach. Said cutting block provide slots that are at fixed distances and angles from one another so that one cutting block must be provided for each size and shape of the implant. The plane of the slot is also fixed so it cannot be modified once the block is affixed to the bone. The accuracy of the cut is proportional to how steady is the hand of the surgeon as well clearance of the blade in the slot. The blade is flexible and can bend if levered in the slot causing the cutting tip of the blade to deflect. This will lead to a change in the plane of the cut and subsequently lead to discrepancy in the press fit of the implant. Obviously, this is more significant and crucial for non-cemented implants.
In these respects, the bicondylar knee resurfacing prosthesis according to the present invention substantially departs from a conventional concepts and designs of the prior art, and in so doing provides an implant that is specifically designed to be inserted through a mini direct true lateral approach without any damage to the patellar tendon, quadriceps mechanism or the cruciate ligaments.
A significant advantage provided by the System of this invention is in using an electromagnetic bone chipper device guided by surgical polygonal cutting blocks having an inverted T slots or channels rather than straight slots. Said inverted T channels are much more precise than the straight slots of conventional cutting blocks. Furthermore, the shank of the electromagnetic bone chipper device used to perform the bone resection is thicker and will not deflect or bend if accidently levered by the operating surgeon.